The present invention relates to a crystal modification of magnesium salt of mono-p-nitrobenzyl malonate and a process for producing the same.
Magnesium salt of mono-p-nitrobenzyl malonate is an important intermediate as a starting material of pharmaceuticals.
Magnesium salt of mono-p-nitrobenzyl malonate cannot be obtained by merely adding magnesium hydroxide to mono-p-nitrobenzyl malonate.
As conventional methods of producing magnesium salt of mono-p-nitrobenzyl malonate, the method of reacting mono-p-nitrobenzyl malonate with magnesium ethoxide in tetrahydrofuran, and further adding ethyl ether thereto is disclosed in, for example, Japanese Patent Application Laid-Open (KOKAI) Nos. 57-159761 (1982) and 58-208292 (1983). This method, however, has problems as far as manufacturing is concerned that magnesium ethoxide is expensive and that a special solvent such as tetrahydrofuran and ethyl ether is necessary. The crystal obtained by the conventional method is a crystal modification of magnesium salt of mono-p-nitrobenzyl malonate (hereinunder referred to as ".alpha.-type crystal", see FIG. 1) which is characterized by an X-ray diffraction pattern having strong peaks at angles of diffraction of (2.theta.) [.degree.] 5.6 and 16.3 according to X-ray diffractometry with Cu-K.alpha. line, and is liable to contain impurities such as by-produced ethyl p-nitrobenzyl malonate, thereby making purification difficult.
As described above, the conventional method has problems such as the use of an expensive material, necessity for a special solvent and difficulty in adequate purification of a crystal modification obtained.
Accordingly, development of an industrial manufacturing method and a crystalline modification free from the above-described problems is demanded.
As a result of studies undertaken by the present inventors so as to eliminate these problems, the present invention has been achieved.